An active matrix substrate includes, e.g., thin film transistors (hereinafter also referred to as “TFTs”) as switching elements, one for each pixel, which is the smallest unit of an image.
A typical bottom-gate TFT includes, for example: a gate electrode provided on an insulating substrate; a gate insulating film provided to cover the gate electrode; an island-like semiconductor layer provided on the gate insulating film to lie above the gate electrode; and a source electrode and a drain electrode provided on the semiconductor layer to face each other.
Furthermore, in recent years, for active matrix substrates, it has been proposed to use, instead of a conventional thin film transistor including a semiconductor layer of amorphous silicon, a TFT including a semiconductor layer of an oxide semiconductor that is an In—Ga—Zn—O (IGZO) oxide semiconductor with high mobility (hereinafter also referred to as an “oxide semiconductor layer”) as a switching element for each pixel, which is the smallest unit of an image.
It is difficult for a thin film transistor using an oxide semiconductor to maintain high thin film transistor performance, and needs exist for controlling the amount of oxygen deficiency due to oxidation annealing and reducing the defect level.
To address this problem, for example, as described in PATENT DOCUMENT 1, process steps of a thermal oxidation annealing process from the placement of a substrate in a diffusion furnace to a heat treatment process (of increasing, stabilizing, and decreasing the furnace temperature) have been conventionally known to be performed in atmospheric gas (nitrogen, oxygen, and water vapor) in the diffusion furnace.
Furthermore, such a multistage glass substrate calcining furnace as described in PATENT DOCUMENT 2 has been known. The multistage glass substrate calcining furnace has a furnace body made of a heat insulator, and includes infrared radiation plates that are vertically arranged with an air gap formed on the inner wall of the furnace body, and between which a plane heater is sandwiched. One of the infrared radiation plates has a gas feed hole, and the other infrared radiation plate has an exhaust hole. Several infrared radiation plates between each adjacent pair of which a plane heater is sandwiched in a manner similar to that in which the plane heater is sandwiched between the right and left infrared radiation plates are horizontally arranged at a predetermined distance apart from one another, and support bars support a glass substrate in a space between each adjacent pair of the horizontal infrared radiation plates.